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Towards 78Ni:In-beam γ-ray spectroscopy of the exotic

nuclei close to N=50

IPN Orsay:D. Verney, M. Niikura, F. Aziez, S. Franchoo, F. Ibrahim, F. Le Blanc, I. Matea, I. Stefan

CSNSM Orsay:A. Korichi

GANIL Caen:L. Càceres, E. Clément, G. De France, S. Grévy, O. Solin

IPHC Strasbourg:F. Didierjean, G. Duchene

LPSC Grenoble:G. Simpson

LNL-INFN LegnaroG. De Angelis, E. Sahin, J.J. Valiente Dobon

AGATA Istanbul workshop6th May 2010

Physics case: Study of shell structure above 78Ni

2

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Zn78Zn77Zn76

Ni74 Ni76Ni75

Ge83

As84

Se85 Se86

Ge84

Se80 Se82

Br81

Kr82 Kr84Kr83

Rb85

Sr86 Sr87

Zn79

Ni76

Cu75

Se84

50

28

Zr92 Zr94 Zr96

Known p

art of

the

valen

ce sp

ace

Unknown p

art of t

he

valen

ce space

Proton single particles

d5/2 d3/2s1/2 g7/2

Neutron single particles

f5/2

p3/2

p1/2

g9/2

OK

OK

?

π-ν Residual

interaction

• Is 78Ni a good core? Persistence of Z=28 and N=50, pair promotions from the lower shells

• What is the nature of valence space which opens up just above ? single particle sequence


Is 78Ni good core?

3

Probably yes...

• O. Sorlin, M. Porquet Prog. Part. Nucl. Phys. 61 (2008) 602

from binding energies of the states blow and above Z=28 and N=50

N=50 gap extrapolation → 78Ni =3.0(5) MeV

100Sn

78Ni

78Ni

56Ni

Z=28 gap extrapolation → 78Ni =2.5 MeV

• from B(E2) measurement in 80Zn (REX-ISOLDE)J. Van de Walle et al. PRC 79, 014309 (2009)«No direct evidence is found for an enhanced Z = 28 core polarization, but the larger proton effective charge needed in the SMI calculations to describe N = 50 isotones with Z < 40 indicate a larger proton core polarization for these isotopes. No evidence is found for breaking of the N = 50 shell gap. »

• from Yrast structure studies from DIC experiments (Legnaro) down to 82Ge Y. H. Zhang et al. PRC 70, 024301 (2004) and subsequent studies E. Sahin et al.« The generally good agreement obtained between calculated and measured level energies in all the cases considered is taken as an argument for the proper description of such semi magic nuclei within the shell-model framework and therefore of the persistence of the N=50 closed shell down to Z=32. »

• from β-decay studies down to 81Ga (Orsay)O. Perru et al. Eur. Phys. J. A 28, 307 (2006)D. Verney et al. PRC 76, 054312 (2007)

• from mass measurements down to 80Zn (IGISOL Jyvaskyla)J. Hakala et al. PRL 101, 052502 (2008)« The data indicates the persistence of this gap towards Ni (Z =28) with an observed minimum at Z=32. »

maybe not...


N=50 shell gap has local minimum at Ge

4

Two neutron separation energyΔ=S2n(52)-S2n(50)

↓N=50 shell gap

Local minimum at Ge (Z=32)

J. Hakala et al. PRL 101, 052502 (2008)


Increasing collectivity toward N=50 in Ge isotope

5

Ge isotopes

Sphericalvibration

“γ-soft”nucleus

Triaxial rotationProlate

vibration

N=48

0.1 0.2 0.3 0.40

80Ge

0.1 0.2 0.3 0.40

N=4678Ge

0.1 0.2 0.3 0.40

N=4476Ge

0.1 0.2 0.3 0.40

N=4274Ge

N=50

“γ-soft”nucleus

HFB D1S Gogny + GCM:O. Perru, J. Libert and D. Girod


What is the nature of valence space above 78Ni?

6

E (MeV)

0.00

1.00

2.453.04

82Neutron single particles

T.A. Hughes, Phys. Rev. 181, 1586 (1969)

d5/2

d3/2

s1/2

g7/2

50

in 89Sr

? h11/2

Shell model calc. with 78Ni coreK. Sieja et al. PRC 79, 064310 (2009)

Duflo Zuker

PRC 59, R2347 (1999)


0

500

1000

1500

2000

2500

3000

Exci

tatio

n en

ergy

[keV

]

7

N=51 isotone systematic

89Sr(Z=38)

87Kr(Z=36)

85Se(Z=34)

83Ge(Z=32)

81Zn(Z=30)

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Ge83

As84

Se85

Sr87

Zn79

Ni77

50

Zn81

Kr87

Sr89

7/2+

7/2+

1/2+

5/2+

3/2+ 50

d5/2s1/2d3/2g7/2

g9/2p1/2

2+ d3/2

or g7/2?

79Ni(Z=28)

?

AGATA Istanbul workshop6th May 2010 8

0

500

1000

1500

2000

Exci

tatio

n en

ergy

[keV

]

N=49 isotone systematics

87Sr(Z=38)

85Kr(Z=36)

83Se(Z=34)

81Ge(Z=32)

79Zn(Z=30)

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Ge83

As84

Se85

Sr87

Zn79

Ni77

50

Kr85

Se83

Ge81

1/2+

5/2+

1/2-

9/2+

3/2+

50

d5/2s1/2d3/2g7/2

g9/2p1/2

77Ni(Z=28)

R.A.Meyer et al., PRC 25 (1982) 682

??


Valence space for proton in west part of 78Ni

T. Otsuka et al. PRL95, 232502 (2005)

K. Flanagan et al., PRL 103, 142501 (2009)

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Ge83

As84

Sr87

Zn79

Ni77

50

Cu77Cu76Cu75Cu74Cu73Cu72Cu71Cu70Cu69 Cu78


Valence space for proton in north part of 78Ni

10

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Ge83

As84

Sr87

Zn79

Ni77

50

the observed structure of the odd-proton N=50 isotones should only (and naturally) reflects the change of the Fermi level to be checked experimentally

From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988)

E (MeV)

-14,386

-13,233

-11,831

-7,121

40

f5/2

p3/2

p1/2

g9/2

Proton single particles

28

50


Proposed experimental setup

11

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Ge83

As84

Se85

Ni77

50

Zr89

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K&?&)!)4'2&4%!3,(*4'&*!+7!@9K$<%I!M(,!7C&!(**K&?&)!+)*!(**K(**!'+%&%!%4'C!&%71/+71()%!+,&!/(,&!*1551'427!

7(!/+H&!+%!7C&-!0122!%7,()62-!*&3&)*!()!7C&!/+1)! K*&'+-!3+7C%I!])!7C&!(?&,+22U!17!1%!%&&)!7C+7!+!2+,6&!

3+,7! (5! 7C&! )4'2&1! ,&3,&%&)7&*! 1)! M16I! F!0(42*! .&'(/&! ,&+'C+.2&! 5(,! K%3&'7,(%'(3-I!S(7&! 7C+7! 1)!7C(%&!'()*171()%!^#S1!0(42*!.&!+7!7C&!21/17!(5!5&+%1.1217-I!!

!!"#$%&'(')*+&,-&.'+%/.$,-"/0'%1-&2',3/2&'-/'4567'10.'859:'

#$"%!GI8I@9F!33%!GG9!:&;<4!

O&'()*+,-!5,+6/&)7%!

V_RR"!

324)6&,!P(371()+2Q!

O&'()*+,-!7+,6&7!PE&Q!

"\!

Ni76

FRS + AGATA + LYCCAsecondary fragmentation reaction86Kr (550 MeV/u, 1.0x1010 pps) on 9Be target (4011 mg/cm2)83As (220 MeV/u, 2.5x104 pps) on 9Be target (2650 mg/cm2)

Zn79Zn78

Ga80Ga79

Ge81

Ni75Ni74

Cu75


Yield estimation (preliminary)

12

Zr90 Zr91

Y89

Sr88

Rb87

Kr86

Br85

Se84

As83

Ge82

Ga81

Zn80

Cu79

Ni78

Ge83

As84

Se85

Ni77

50

Zr89

Ni76

Cu78Cu77

Zn79Zn78

Ga80Ga79

Ge81

Ni75

Cu76

Ni74

Co75Co74

Zn81

Ga82

Cu75

1.0E-06

1.0E-04

1.0E-02

1.0E+00

1.0E+02

47 48 49 50 51 52

Ge Ga Zn Cu Ni Co

N

Prod

ucti

on r

ate

(pps

)

100 counts/week

• 83As beam (220 MeV/u, 2.5x104 pps)• Be target (2650 mg/cm2)• 15% efficiency for AGATA• all products through 1st to g.s. transition


Summary

We propose to perform the in-beam gamma-ray spectroscopy of very neutron-rich nuclei around N=50 towards 78Ni using the secondary fragmentation reaction of a 83As (Z=33, N=50) beam with FRS + AGATA + LYCCA.

Physics interest

• 78Ni can be considered as a good core for shell model?

• increasing collectivity across N=50 (2+, 4+ sequence)

• shell structure, order of orbit, π-ν interaction

• proton shell seems to be understood by tenser interaction (cf. Cu isotope)

• inversion of g.s. spin from 5/2- to 3/2- between 85Ba and 83As

• decreasing single-particle energy space between νs1/2 and νd5/2

• mysterious of 1/2- state in N=49

13


Down sloping of s1/2 states

15

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